CHRONOMETER, 



Contrivance, by or through which the 

 successive impulscs,or actions, are made, 

 is called a 'scapement or ESCAPEMEXT, 

 several of which are described at the ar- 

 ticles referred to. 



According to the nature of the escape- 

 ment, and the part of the vibrating arc 

 at which the impulses are applied, the 

 vibrations of the balance may be made 

 to employ a longer or shorter time than 

 they would have employed if the balance 

 had'been separate from the works. Thus, 

 in the common watch, these impulses 

 quicken the vibrations ; and consequent- 

 ly an increase in the maintaining force 

 will make the watch go faster ; as may 

 be easily tried by gently forcing the 

 key in the opposite direction to winding 

 up. 



If the balance and its spring were to 

 continue unchanged in all temperatures, 

 and under all circumstances, and if its 

 long and short vibrations measured equal 

 times when separate from the machine, 

 it would only be required that the escape- 

 ment should be so constructed as neither 

 to accelerate nor retard them. But none 

 of these conditions can be had in the or- 

 dinary structure of watches, and in the 

 superior time-pieces considerable diffi- 

 culties are found in the attempt to obtain 

 them. 



By the natural contraction, to which all 

 bodies are subject when cooled, the di- 

 ameter of the balance will be less the 

 lower the temperature : it will therefore 

 be more easily carried by the vibrating 

 forces, and will then vibrate more quick- 

 ly- 



The spring attached to the balance, 

 which is called the pendulum spring, will 

 likewis^ act with greater force when 

 cold, and on this account also the vibra- 

 tions will be quicker. 



The remedies for these causes of im- 

 perfection are the following: 



1. The Remontoire. As the irregu- 

 larities in the transmission of force from 

 the main spring are certainly increased 

 by the number of wheels in the train, it 

 was proposed, in the infancy of the art, 

 to detach the last wheel, or that nearest 

 the balance, or time measurer, from the 

 rest, and to move this by a separate spring 

 or weight: so that in this contrivance the 

 time measurer is acted upon by one single 

 wheel, and the rest of the train is employ- 

 ed in winding up the secondary first 

 mover at short intervals, such, for exam- 

 ple, as every half minute. We shall also 

 have to mention some escapements, in 

 which the winding up is performed in 



every single vibration. With regard to 

 remontoires, it may be remarked, that 

 they either greatly shorten, or else de- 

 stroy the periodical irregularities of the 

 train, and those of the main-spring; but 

 that with regard to the innuence of oil, 

 and other causes of more permanent dif- 

 ference, their advantage is not very con- 

 siderable, because the remedy is not ap- 

 plied where the motion is quickest. 



Whether the irregular action of the 

 maintaining power be diminished by the 

 remontoire or not, it is desirable that the 

 impulse on the balance, through the es- 

 capement, should affect the natural mea- 

 sure of its vibrations as little as possible; 

 or rather that it should tend to equalise 

 them when the arcs of vibration vary. 

 Some attention, but not much, has been 

 paid to the equalizing quality of an es- 

 capenifnt, principally by making the 

 faces of the pallets of a figure suitable to 

 that effect ; but these are now for the 

 most part abandoned, and the method of 

 applying the force constitutes the dis- 

 tinguishing feature in this part of our mo- 

 dern chronometers. If a balance be set 

 to vibrate by the mere action of its pen- 

 dulum spring, its motion will soon de- 

 cay ; but if we suppose a lever or pallet 

 to proceed from its axis, and a maintain- 

 ing power to be applied to this, it is ob- 

 vious, that if the power meet the pallet in 

 its progress from the point of quiescence, 

 it will shorten the time, and also the arc 

 of that semi-vibration ; and, again, that if 

 the power follow the pallet in its pro- 

 gress towards the point of quiescence, it 

 will drive it home sooner, and conse- 

 quently will shorten the time of that se- 

 mi-vibration; and that actions contrary to 

 these would lengthen the times. If,there- 

 fore, the action itself, which may be con- 

 sidered as an accelerating force, be not 

 applied on both sides of the point of qui- 

 escence through a certain arc, determin- 

 able from the circumstances, the main- 

 taining power, when it comes to be ap- 

 plied, will alter the time ; and if this va- 

 ry, the time must also vary. Now the 

 remedy at present adopted is, to make 

 the balance vibrate through a very large 

 arc, such as a semicircle or more, and to 

 follow the pallet in each returning vibra- 

 tion by a strong power exerted through a 

 very small arc, as, for example, 15 or 

 16. By this contrivance the balance will 

 vibrate at perfect liberty, out and home, 

 through two semicircles, or 360, except- 

 ing the small part during which the im- 

 pulse is given; and if the impulse vary, 

 the arc of vibration will vary, and with it 



